The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Continuous media recording systems write data to a disk that is coated by magnetic material in a continuous pattern. Prior to a write operation, servo sector information (e.g., preamble data, synchronization marks, and positioning information) is read from a disk. The servo sector information is used to position a read/write head and to correct head positioning error. Head positioning error may refer to a difference between (i) the true track/data bit position on a disk that data is stored (or is to be stored) and (ii) the read/write head position on the disk at which the data is to be read and/or written. Subsequent to correcting head positioning error, data is written to sectors of the disk at a desired position. Since data is written to the disk with continuous magnetic material pattern in a track, the data may be written generally at any point within a sector of the disk.
In continuous media, bits are stored in adjacent locations on a disk. Each bit is stored in multiple independent grains (nanometer-scale grains) in a film of magnetic alloy. The size of the grains may be reduced to increase bit density on a disk. The smaller the size of the grains, the more interference between the grains due to a superparamagnetic effect. The superparamagnetic effect refers to magnetization flipping of grains due to changes in, for example, temperature. The superparamagentic effect can negatively affect maintenance of data and thus limit storage density of a disk.
Bit-patterned media (BPM) recording systems provide increased storage capacity over continuous media recording systems. BPM recording systems may store as much as ten times more information on a magnetic storage device (e.g., a magnetic disk or hard disk) than continuous media recording systems. As an example, a BPM recording system may store 1 or more terabits (Tbit) of data in one square inch (in2) of a magnetic disk.
BPM recording systems write data to a disk in discontinuous island-based patterns (uniform magnetic islands on the disk surface). Bits of data are stored at specific points or discrete bit islands on the disk. The bit islands are separated by grooves and/or non-magnetic material(s). For example, each bit island may store 1 bit of data. As each bit is stored on a designated bit island, thermal stability of BPM can be better than thermal stability of continuous media. Also, interference between bit islands of BPM is less than interference between grains in continuous media.
Bit-level head positioning accuracy requirements of BPM recording systems are more stringent than that of continuous media recording systems, as bit positions on BPM (or bit island locations) are predefined. Accurate bit-level head positioning ensures that data is written over correct bit islands of a disk while minimizing and/or avoiding attempts to write data over areas between bit islands (or to wrong bit islands).
A BPM recording system may include a write clock. The write clock may be used for timing write events including positioning and access timing of a write head. Synchronization of the write clock with the patterned media is needed in a BPM recording system due to the discontinuous format of BPM. A write clock signal is synchronized when rising and/or falling edges of the write clock signal are aligned with start and end positions of the bit islands, such that writing occurs over the bit islands and not over areas between bit islands. Loss in synchronization between the write clock signal and the bit islands can lead to errors, which may be difficult to detect and correct.